Well...The IDF operates in terms of constant severe money shortage. And the same units that fight in the desert have to fight in the north, and in urban terrain. Dark olive green is the best all around, espcially in the dark. Its not as good for every specific area of Israel, but all around it dose well. Specific units of course use other uniforms, including american camo, white snow camo, etc.
So mostly its an economic issue.